1. Field of the Invention
The present invention relates to a reactive coating composition and to the treatment of a surface containing heavy metals by coating the surface with the reactive coating composition. The surface can include a paint layer containing heavy metals. Stabilizing agents within the coating composition penetrate the paint layer upon contact to stabilize the heavy metals. The coating composition dries and remains adhered to the paint layer to form a treated paint layer having reduced leachability. The reactive coating composition can be applied onto a painted surface to adhere and stabilize heavy metals contained in the painted surface, with or without the removal of the treated paint layer from the surface.
2. Description of Related Art
Many older structures have been coated with a paint that includes one or more heavy metals, such as a lead-based paint. These heavy metals are now recognized as being harmful to animals and humans, even in small quantities. As such, the lead-based paint layers must be treated to minimize the environmental risks associated with the lead.
Lead-based paint layers and other heavy metal-containing layers are found on and around metal, wooden or concrete structures such as bridges, storage tanks and towers, dock yards, military installations, industrial facilities and commercial/residential buildings. Many roadways and parking lots have also been painted with lead-based paint compositions. Government regulations require the removal of the lead-based paint layer and/or disposal of the materials coated with the lead-based paint in a manner that minimizes the environmental risk.
There have been many attempts in the prior art to stabilize heavy metals, such as lead in lead-based paints. Some methods contemplate the treatment of the material either during or after generation of paint waste by removing the paint from the painted structure. For example, U.S. Pat. No. 5,911,838 by Barnett discloses the application of an aqueous solution to a painted surface, where the solution includes a solvent, a film former, a viscosity builder and an alkaline compound. The solution causes the paint to coagulate and separate from the substrate such that the paint can be stripped from the substrate. The stripped paint must then be treated to convert the lead to an insoluble form, or it must be disposed as a hazardous waste.
U.S. Pat. No. 6,186,939 by Forrester discloses that heavy metals can be complexed when exposed to natural or induced leaching conditions by contacting a stabilizing agent with paint particles as the paint particles are generated into paint waste by sandblasting the paint from a surface. It is also disclosed that the paint surface can be coated with a stabilizing agent prior to removal of the paint to generate a paint waste. U.S. Pat. No. 6,050,929 by Forrester also discloses that heavy metals can be complexed when exposed to natural or induced leaching conditions by contacting a stabilizing agent with the paint particles as the paint particles are generated by sandblasting.
U.S. Pat. No. 5,667,696 by Studer et al. discloses that a stabilizing agent such as triple superphosphate (TSP) can be mixed with paint waste to stabilize the heavy metals contained in the paint waste.
U.S. Pat. No. 5,674,108 by Rolle discloses compositions for removing coatings such as lead-based paints. A treatment layer is applied that includes a material such as one selected from compounds of sodium and potassium silicates, sodium and potassium phosphates, calcium silicate, iron and aluminum sulfates and also includes an alkaline metal salt. The treatment layer is then removed from the substrate along with the underlying coating. U.S. Pat. No. 6,089,955 by Rolle et al. discloses a method for removing a coating on a surface by applying a treatment composition layer made up of a first material selected from compounds of sodium and potassium silicates, sodium and potassium phosphate, calcium silicate, iron and aluminum sulfates.
U.S. Pat. No. 6,001,185 by Huff discloses that a material such as calcium phosphate can be added to paint or other surface coatings and applied over a previously applied heavy metal contaminated paint. It is disclosed that the finely ground calcium phosphate compounds in the new coating react with the heavy metal compound in the contaminated paint to render the heavy metal compound immobile and biologically non-hazardous.
U.S. Pat. No. 5,637,355 by Stanforth et al. also discloses that additives can be added to a standard commercial paint and the mixture can be sprayed onto a lead-bearing paint surface. The paint and coating are then removed from the surface such as by sand-blasting. U.S. Pat. No. 5,902,392 by Henkelman et al. discloses a similar composition and method.
However, a method for the stabilization of lead-based paint on the existing material surface that permits: (i) the removal of the non-hazardous material coating and continued use of the structure; (ii) the application of standard coatings (e.g., paint) over the stabilized heavy metal coating; or (iii) the disposal of the material and structure as non-hazardous debris in a cost effective manner, has eluded the environmental industry.
Many older structures have been re-painted many times with lead-based paint without removal of the previous paint layer and therefore the paint is often very thick and the heavy metal concentration is high. In addition, most lead-based paint layers have been painted over with paint that does not include heavy metals, preventing direct surface access to the lead-based paint layer. Further, when the lead-based paint is applied to wood, some of the paint may be absorbed into the wood, making it difficult to remove all of the lead-based paint by sanding or scraping without removing a significant amount of the underlying wood. The generation of paint waste by removing the paint can also create a fine dust that can carry the heavy metals into the environment if the dust is not suppressed.
There remains a need for an improved coating composition for the treatment of paint layers including a heavy metal, such as those formed from lead-based paints. It would be advantageous if such a coating had strong adherence to the paint layer and did not require the generation of a hazardous paint waste by removing the paint from the surface prior to disposal. It would also be advantageous to provide a coating composition that can be applied to a paint layer and is capable of reacting with the heavy metals in the paint layer to fixate the heavy metals, reducing their leachability and enabling the structure to remain in place, or minimizing the release of lead-based paint into the air, soil and work site during demolition activities.